ORGANIZATION AND CONTROL OF ENDOCRINE SYSTEM ENDOCRINE SYSTEM

uses chemical substances called hormones as a means of regulating and integrating body functions.

participates in the regulation of digestion, use, and storage of nutrients; growth and development electrolyte and water metabolism; and reproductive functions.

functions of the endocrine system are closely linked with those of the nervous system and the immune system and functions of the immune system also are closely linked with those of the endocrine system. The immune system responds to foreign agents by means of chemical messengers (cytokines,

e.g., interleukins, interferons) and complex receptor mechanisms .The immune system also is extensively regulated by hormones such as the adrenal cortico steroid hormones

ANATOMY OF ENDOCRINE SYSTEM

The primary glands that make up the human endocrine system are the

hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal body, and reproductive glands—the ovary and testis.

In addition, some nonendocrine organs are known to actively secrete hormones. These include the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta.

Almost all body cells can either produce or convert hormones, and some secrete hormones. For example, glucagon, a hormone that raises glucose levels in the blood when the body needs extra energy, is made in the pancreas but also in the wall of the gastrointestinal tract.

HORMONES -are chemical messengers created by the body where they transfer information from one set of cells to another to coordinate the functions of different parts of the body. - specific messenger molecule synthesized and secreted by a group of specialized cells called an endocrine gland. PHEROMONES - also communication chemicals, but are used to send signals to other members of the same species. ENDOCRINE GLAND -ductless - their secretions (hormones) are released directly into the bloodstream and travel to elsewhere in the body to target organs, upon which they act. EXOCRINE GLAND -not part of the endocrine system that secrete products that are passed outside the body.

-Sweat glands, salivary glands, and digestive glands are examples of exocrine glands.

The roles of hormones in selecting target cells and delivering the hormonal message. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.

HORMONE RECEPTORS -binding sites on the target cells Each hormone’s shape is specific and can be recognized by the corresponding target cells. Many hormones come in antagonistic pairs that have opposite effects on the target organs. For example, insulin and glucagon have opposite effects on the liver’s control of blood

sugar level. Insulin lowers the blood sugar level by instructing the liver to take glucose out of circulation and store it, while glucagon instructs the liver to release some of its stored supply to raise the blood sugar level. Much hormonal regulation depends on feedback loops to maintain balance and homeostasis. CHARACTERISTICS OF HORMONES A single hormone can exert various effects in different tissues or, conversely, a single function can be regulated by several hormones. ■Hormones function as chemical messengers, moving through the blood to distant target sites of action, or acting more locally as paracrine or autocrine messengers that incite more local effects. ■Most hormones are present in body fluids at all times but in greater or lesser amounts, depending on the needs of the body. ■Hormones exert their actions by interacting with high affinity receptors, which in turn are linked to one or more effectors systems in the cell. Some hormone receptors are located on the surface of the cell and act through second messenger mechanisms ,and others are located in the cell, where they modulate the synthesis of enzymes, transport proteins, or structural proteins

THREE GENERAL CLASSES OF HORMONES

These are classified by chemical structure, not function.

steroid hormones including prostaglandins which function especially in a variety of female functions (aspirin inhibits synthesis of prostaglandins, some of which cause “cramps”) and the sex hormones all of which are lipids made from cholesterol,

amino acid derivatives (like epinephrine) which are derived from amino acids, especially tyrosine, and

peptide hormones (like insulin) which is the most numerous/diverse group of hormones.

Local regulators -hormones with target cells nearby or adjacent to the endocrine gland in question. For example, neurotransmitters are secreted in the synapses of our nervous system and their target cells are in the same synapses. NONSTEROID HORMONES - water soluble -do not enter the cell but bind to plasma membrane receptors, generating a chemical signal inside the target cell. STEROID HORMONES

-pass through the plasma membrane and act in a two step process. Steroid hormones bind, once inside the cell, to the nuclear membrane receptors, producing an activated hormone-receptor complex. The activated hormone-receptor complex binds to DNA and activates specific genes, increasing production of proteins. Paracrine and Autocrine Actions-some hormones and hormone-like substances never enter the blood-stream but instead act locally in the vicinity in which they are released. Paracrine - act locally on cells other than those that produced the hormone, action of sex steroids on the ovary is a paracrine action. Autocrine - Hormones also can exert anautocrine action on the cells from which they were produced. For example, the release of insulin from pancreatic beta cells can inhibit its release from the same cells. Juxtacrine -refers to a mechanism whereby a cytokine that is em-bedded in, bound to, or associated with the plasma membraneof one cell interacts with a specific receptor in a juxtaposed cell. Eicosanoids and Retinoids- group of compounds that have a hormone-like action arethe eicosanoids, which are derived from polyunsaturated fatty acids in the cell membrane. EICOSANOIDS- arachidonic acid is the most important and abundant precursor of the various eicosanoids. - most important of the eicosanoids are the prostaglandins, leukotrienes, and thromboxanes. (these fatty acid derivatives are produced by most body cells, are rapidly cleared from the circulation, and are thought to act mainly by paracrine and autocrine mechanisms.) - Synthesis often is stimulated in response to hormones, and they serve as mediators of hormone action. Retinoids (e.g., retinoic acid) also are derived from fatty acids and have an important role in regulating nuclear receptor action. MAJOR HORMONES

Hormone Gland Origin Target Tissue Function

Adrenocorticotropic Pituitary gland (anterior)

Adrenal cortex Triggers secretion of hydrocortisone from the adrenal gland

Growth hormone Pituitary gland (anterior)

Throughout body Stimulates growth and development

Follicle-stimulating hormone

Pituitary gland (anterior)

Sex glands Stimulates female egg maturation and male sperm production

Luteinizing hormone Pituitary gland (anterior)

Sex glands Stimulates female ovulation and male secretion of testosterone

Prolactin Pituitary gland (anterior)

Mammary glands Stimulates milk production in the breasts after childbirth

Thyroid-stimulating hormone

Pituitary gland (anterior)

Thyroid gland Triggers secretion of thyroid hormones

Melanocyte-stimulating hormone

Pituitary gland (anterior)

Melanin-producing cells

Controls skin pigmentation

Antidiuretic hormone Pituitary gland (posterior)

Kidneys Regulates water retention and blood pressure

Oxytocin Pituitary gland (posterior)

Uterus Mammary glands

Triggers contraction of the uterus during labor Stimulates milk letdown for breast-feeding after childbirth

Melatonin Pineal gland Unclear, although possible target sites are pigment cells and sex organs

May affect skin pigmentation; may regulate biorhythms (awake/sleep patterns) and prevent jet lag

Calcitonin Thyroid gland

Bones Controls the level of calcium in the blood by depositing it in the bones

Thyroid hormone Thyroid gland

Throughout body Increases the body's metabolic rate; promotes normal growth and development

Parathyroid hormone Parathyroid glands

Bones, intestines, and kidneys

Regulates calcium level in blood

Thymosin Thymus White blood cells Promotes the growth and development of white blood cells, helping the body fight infection

Aldosterone Adrenal gland

Kidneys Regulates sodium and potassium levels in the blood to control blood pressure

Hydrocortisone Adrenal gland

Throughout body Plays key role in stress response; increases blood glucose levels and mobilizes fat stores; reduces inflammatation

Epinephrine Adrenal gland

Muscles and blood vessels

Increases blood pressure, heart and metabolic rate, and blood sugar levels; dilates blood vessels. Also released during exercise

Norepinephrine Adrenal gland

Muscles and blood vessels

Increases blood pressure and heart rate; constricts blood vessels

Glucagon Pancreas Liver Stimulates the breakdown of glycogen (stored carbohydrate) into glucose (blood sugar); regulates glucose blood level

Insulin Pancreas Throughout body Regulates blood glucose levels; increases storage of glycogen; facilitates glucose intake by body cells

Estrogen Ovaries Female reproductive system

Causes sexual development and growth; maintains proper functioning of female reproductive system

Progesterone Ovaries Mammary glands Uterus

Prepares uterus for pregnancy

Testosterone Testes Throughout body Causes sexual development and growth spurt; maintains proper functioning of male reproductive system

Erythropoietin Kidney Bone Marrow Produces red blood cells

Hormones Regulated by the Hypothalamic/Pituitary System

Hormone Pituitary Stimulating

Hormone

Hypothalamic Releasing Hormone

Thyroid hormones T4, T3 Thyroid-stimulating hormone (TSH)

Thyrotropin-releasing hormone (TRH)

Cortisol Adrenocorticotropin hormone (ACTH)

Corticotropin-releasing factor (CRF)

Estrogen or testosterone Follicle-stimulating hormone (FSH), luteinizing hormone (LH)

Luteinizing hormone-releasing hormone (LHRH) or gonadotropin-releasing hormone (GnRH)

Insulinlike growth factor-I (IGF-I)

Growth hormone Growth hormone-releasing hormone (GHRH)

Hormones of the Anterior Pituitary Hormone Secreted by Releasing Hormone

(Stimulates Secretion) Inhibiting Hormone (Suppresses Secretion)

Human growth hormone (hGh) or somatotropin

Somatotrophs Growth hormone-releasing hormone (GHRH), also known as somatocrinin.

Growth hormone-inhibiting hormone (GHIH), also known as somatostatin.

Thyroid-stimulating hormone (TSH) or thyrotropin

Thyrotrophs Thyrotropin-releasing hormone (TRH)

Growth hormone-inhibiting hormone (GHIH).

Follicle stimulating hormone (FSH)

Gonadotrophs Gonadotropic-releasing hormone (GnRH)

-

Luteinizing hormone (LH) Gonadotrophs Gonadotropic-releasing hormone (GnRH)

-

Prolactin (PRL) Lactotrophs Prolactin-releasing hormone (PRH); TRH.

Prolactin-inhibiting hormone (PIH), which is dopamine.

Adrenocorticotropic hormone (ACTH) or corticotropin

Corticotrophs Corticotropin-releasing hormone (CRH).

-

Melanocyte-simulating hormone (MSH)

Corticotrophs Corticotropin-releasing hormone (CRH).

Dopamine.

Principal Actions of Anterior Pituitary Hormones Hormone Target Tissues Principal Actions Human growth hormone (hGh) or somatotropin

Liver Stimulates liver, muscle, cartilage, bone and other tissues to synthesize and secrete insulinlike

growth factors (IGFs); IGFs promote growth of body cells, protein synthesis, tissue repair, lipolysis, and elevation of blood glucose concentration.

Thyroid-stimulating hormone (TSH) or thyrotrophin

Thyroid gland Stimulates synthesis and secretion of thyroid hormones by thyroid gland.

Follicle stimulating hormone (FSH)

Ovaries, Testes In females, initiates development of oocytes and induces ovarian secretion of estrogens. In males, stimulates testes to produce sperm.

Luteinizing hormone (LH) Ovaries, Testes In females, stimulates secretion of estrogens and progesterone, ovulation and formation of corpus luteum. In males, stimulates interstitial cells in testes to develop and produce testosterone.

Prolactin (PRL) Mammary glands Together with other hormones, promotes milk secretion by the mammary glands.

Adrenocorticotropic hormone

Adrenal Cortex Stimulates secretion of glucocorticoids (mainly cortisol) by adrenal cortex.

Melanocyte-simulating hormone (MSH)

Brain Influence brain activity; when present in excess, can cause darkening of skin.

Posterior Pituitary Hormones Hormone Target Tissues Control of Secretion Principal

Actions Oxytocin (OT) Uterus, Mammary

glands Neurosecretory cells of hypothalamus secrete OT in response to uterine distention and stimulation of nipples.

Stimulates contraction of smooth muscle cells of uterus during childbirth; stimulates contraction of myoepithelial cells in mammary glands to cause milk ejection.

Antidiuretic hormone (ADH) or vasopressin

Kidneys, Sudoriferous (sweat)

Neurosecretory cells of hypothalamus secrete ADH in

Conserves body water by

glands, Arterioles response to elevated blood osmotic pressure, dehydration, loss of blood osmotic pressure dehydration, loss of blood

decreasing urine volume; decreases water loss tgrough perspiration; raises blood pressure by constricting arterioles.

volume, pain or stress; low blood osmotic pressure, high blood volume, and alcohol inhibit ADH secretion. Thyroid Gland Hormones Hormone Source Control of Secretion Principal

Actions T3 (triiodothyronine) and T4 (thyroxine) or thyroid hormones from follicular cells

Thyroid follicle → Follicular cells

Secretion is increased by thyrotropin-releasing hormone (TRH), which stimulates release of thyroid-stimulating hormone (TSH) in response to low thyroid hormone levels, low metabolic rate, cold, pregnancy, and high ltitudes; TRH and TSH secretion are inhibited in response to high thyroid hormone levels; high iodine level suppresses t3/t4 secretion.

Increase basal metabolic rate, stimulate synthesis of proteins, increase use of glucose and fatty acids for ATP production, increase lipolysis, enhance cholesterol excretion, accelerate body growth, and contribute to development of the nervous system.

Calcitonin (CT) from parafollicular cells accelerating

Thyroid follicle → Parafollicular cells

High blood Ca2+ levels stimulate secrewtion; low blood Ca2+ levels inhibit secretion.

Lowers blood levels of ionic calcium and phosphates by inhibiting bone resorption by

osteoclasts and uptake of calcium and phosphates into bone matrix.

Parathyroid Gland Hormone Hormone Source Control Secretion Principal

Actions Parathyroid hormone (PTH)

Chief cells Low blood Ca2+ levels stimulate secretion. High blood Ca2+ levels inhibit secretion.

Increase blood Ca2+ and Mg2+ levels and decreases blood phosphate level; increases bone resorption by osteoclasts; increases Ca2+ reabsorption and phosphate excretion by kidneys; and promotes formation of calcitriol (active form of vitamin D), which increases rate of dietary Ca2+ and Mg2+ absorption.

Hormone and Source Control of Secretion Principal Actions Adrenal cortex hormones Mineralocorticoids (mainly aldosterone) from zona glomerulosa cells

Increased blood K+ level and angiotensin II stimulate secretion.

Increase blood levels of Na+ and water and decrease blood level of K+.

Glucocorticoids (mainly cortisol) from zona fasciculate cells

ACTH stimulates release; corticotropin-releasing hormone (CRH) promotes ACTH secretion in response to stress and low blood levels of glucocorticoids.

Increase protein breakdown (except in liver), stimulate gluconeogenesis and lipolysis, provide resistance to stress, dampen inflammation, and depress

immune responses.

Androgens (mainly dehydroepiandrosterone or DHEA) from zona reticularis cells

ACTH stimulates secretion. Assist in early growth of axillary and pubic hair in both sexes; in females, contribute to libido and are source of estrogens after menopause.

Adrenal medulla hormones Epinephrine and norepinephrine from chromaffin cells

Sympathetic preganglionic neurons release acetylcholine, which stimulates secretion.

Produce effects that enhance those of the sympathetic division of the autonomic nervous system (ANS) during stress.

Pancreatic Hormones Hormone and Source Control of Secretion Principal Actions Glucagon from alpha cells of pancreatic islets

Decreased blood level of glucose, exercise and mainly protein meals stimulate secretion; somatostatin and insulin inhibit secretion.

Raises blood glucose level by accelerating breakdown of glycogen into glucose in liver (glycogenolysis), converting other nutrients into glucose in liver (gluconeogenesis), and releasing glucose into the blood.

Insulin from beta cells of pancreatic islets

Increased blood level of glucose, acetylcholine (released by parasympathetic vagus nerve fibers), argentine and leucine (two amino acids), glucagons, GIP, hGh, and ACTH stimulate secretion; somatostatin inhibits secretion.

Lowers blood glucose level by accelerating transport of glucose into cells, converting glucose into glycogen (glycogenesis), and decreasing glycogenolysis and gluconeogenesis; also increase lipogenesis and stimulates protein synthesis.

Somatostatin from delta cells of pancreatic islets

Pancreatic polypeptide inhibits secretion.

Inhibits secretion of insulin and glucagons and slows absorption of nutrients from the gastrointestinal tract.

Pancreatic polypeptide from F cells of pancreatic islets

Meals containing protein, fasting, exercise, and acute hypoglycemia stimulate secretion; somatostatin and elevated blood glucose level inhibit secretion.

Inhibits somatostatin secretion, gallbladder contraction, and secretion of pancreatic digestive enzymes.

Hormone of the Ovaries and Testes Hormone Principal Actions Ovarian hormones Estrogens and progesterone

Together with gonadotropic hormones of the anterior pituitary gland, regulate the female reproductive cycle, regulate oogenesis, maintain pregnancy, prepare the mammary glands for

lactation, and promote development and maintenance of feminine secondary sex characteristics.

Relaxin Increase flexibility of pubic symphysis during pregnancy and helps dilate uterine cervix during labor and delivery.

Inhibin Inhibits secretion of FSH from anterior pituitary.

Testicular hormones Testosterone

Stimulates descent of testes before birth, regulates spermatogenesis, and promotes development and maintenance of masculine secondary sex characteristics.

Inhibin Inhibits secretion of FSH from anterior pituitary.

Hormones produced by organs and tissues that contain endocrine cells Hormone Principal Actions Gastrointestinal tract Gastrin

Promotes secretion of gastric juice and increases motility of the stomach.

Glucose-dependent insulinotropic peptide (GIP)

Stimulates release of insulin by pancreatic beta cells.

Secretin Stimulates secretion of pancreatic juice and bile. Cholecystokinin (CCK) Stimulates secretion of pancreatic juice,

regulates release of bile from the gallbladder, and brings about a feeling of fullness after eating.

Placenta Human chorionic gonadotropin (hCG)

Stimulates the corpus luteum in the ovary to continue the production of estrogens and progesterone to maintain pregnancy.

Estrogens and progesterone Maintain pregnancy and help prepare mammary glands to secrete milk.

Human chorionic somatomammotropin (hCS) Stimulates the development of the mammary glands for lactation.

Kidneys Erythropoietin (EPO)

Increases rate of red blood cell formation.

Calcitriol* (active form of vitamin D) Aids in the absorption of dietary calcium and phosphorous.

Heart Atrial natriuretic peptide (ANP)

Decrease blood pressure.

Adipose tissue Leptin

Suppresses appetite and may have a permissive effect on activity of GnRH and gonadotropins

PARTS OF THE ENDOCRINE SYSTEM

Illustration of the endocrine system

Hypothalamus - located in the lower central part of the brain. - Part of the brain which is important in regulation of satiety, metabolism, and body temperature. - secretes hormones that stimulate or suppress the release of hormones in the pituitary gland. Releasing Hormones - secreted into an artery (the hypophyseal portal system) that carries them directly to the pituitary gland. -it signals secretion of stimulating hormones.

Somatostatin -it causes the pituitary gland to stop the release of growth hormone.

Pituitary Gland

-located at the base of the brain beneath the hypothalamus and is no larger than a pea. -considered the most important part of the endocrine system because it produces hormones that control many functions of other endocrine glands.

I. ANTERIOR LOBE

Growth hormone: Stimulates growth of bone and tissue (growth hormone deficiency in children results in growth failure. Growth hormone deficiency in adults results in problems in maintaining proper

amounts of body fat and muscle and bone mass. It is also involved in emotional well-being.)

Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones (A lack of thyroid hormones either because of a defect in the pituitary or the thyroid itself is called hypothyroidism.)

Adrenocorticotropin hormone (ACTH): Stimulates the adrenal gland to produce several related steroid hormones

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH): Hormones that control sexual function and production of the sex steroids, estrogen and progesterone in females or testosterone in males

Prolactin: Hormone that stimulates milk production in females

II. POSTERIOR LOBE

Antidiuretic hormone (vasopressin): Controls water loss by the kidneys

Oxytocin: Contracts the uterus during childbirth and stimulates milk production

Thyroid Gland

-located in the lower front part of the neck. -produces thyroid hormones that regulate the body's metabolism.

-plays a role in bone growth and development of the brain and nervous system in children. Thyroid Hormone - help maintain normal blood pressure, heart rate, digestion, muscle tone, and reproductive functions.

Parathyroid Glands

- two pairs of small glands embedded in the surface of the thyroid gland, one pair on each side. - release parathyroid hormone. PARATHROID HORMONE -plays a role in regulating calcium levels in the blood and bone metabolism.

Adrenal Glands - adrenal glands are triangular-shaped glands located on top of each kidney.

ADRENAL CORTEX - outer part that produces hormones called corticosteroids, which regulate the body's metabolism, the balance of salt and water in the body, the immune system, and sexual function. ADRENAL MEDULLA - inner part that produces hormones called catecholamines (for example, adrenaline). These hormones help the body cope with physical and emotional stress by increasing the heart rate and blood pressure.

Pineal Body/ Pineal Gland - located in the middle of the brain. - secretes a hormone called melatonin. MELATONIN - regulate the wake-sleep cycle of the body.

Reproductive Glands - Main source of sex hormones. MALES - the testes, located in the scrotum, secrete hormones called androgens; the most important of which is testosterone. These hormones affect many male characteristics (for example, sexual development, growth of facial hair and pubic hair) as well as sperm production.

FEMALES - the ovaries, located on both sides of the uterus, produce estrogen and progesterone as well as eggs. These hormones control the development of female characteristics (for example, breast growth), and they are also involved in reproductive functions (for example, menstruation, pregnancy).

Pancreas

- Elongated organ located toward the back of the abdomen behind the stomach. - has digestive and hormonal functions. EXOCRINE PANCREAS - secretes digestive enzymes. ENDOCRINE PANCREAS - secretes hormones called insulin and glucagon. These hormones regulate the level of glucose (sugar) in the blood.

HORMONE ACTION

Hormone signals a cell by biding to specific receptors on or in the cell.

“lock-and-key” mechanism (hormones will bind only to receptor molecules that fit them

exactly)

Target cell (any cell with one or more receptors for a particular hormone)

Each different hormone-receptor interaction produces different regulatory changes within

the target cell

Different hormones may work together to enhance each other’s influence on a target cell.

o Synergism- combinations of hormones have a greater effect on the target cell than the

sum of the effects that each would have if acting alone

o Permissiveness- it occurs when a small amount of one hormone allows a second

hormone to have its full effect on a target cell; the first hormone permits the full action of

the second hormone

o Antagonism- seen as the common type of combined action of hormones; one hormone

produces the opposite effect of another hormone; it give signals to the cell when to

increase or decrease a certain cellular process

Mechanism of Steroid Hormone Action

Steroid hormones are lipids and thus are not very soluble in blood plasma, which is mostly

water. Instead of travelling in the plasma as free molecules, they attach to soluble plasma

proteins.

A steroid hormone molecule dissociates from its carrier before approaching the target cell.

Because steroid hormones are lipid-soluble and thus can pass into cells easily, it is not

surprising that their receptors are normally found inside the cell rather than on the surface

of the plasma membrane.

After a steroid hormone

molecule has diffused into its

target cell, it passes into the

nucleus where it binds to a

mobile receptor molecule to form

a hormone-receptor complex.

Some hormones must be

activated by enzymes before

they can bind to their receptors.

Because steroid hormone

receptors are not attached to the

plasma membrane, but seem to

move freely in the nucleoplasm,

this model of hormone action

has been called the mobile-

receptor hypothesis.

Once formed, the hormone-receptor complex activates a certain gene sequence to begin

transcription of messenger RNA (mRNA) molecules.

The newly formed mRNA molecule then move out of the nucleus into the cytosol, where they

associate with ribosomes and begin synthesizing protein molecules.

The new protein molecules synthesized by the target cell would not have been made if not

for the arrival of the steroid hormone molecule. Steroid hormones regulate cells by

regulating their production of certain critical proteins.

This mechanism of steroid hormone action implies several things about the effects of these

hormones. For one thing, the more hormone-receptor complexes formed, the more new

protein molecule are formed, and thus the greater the magnitude of regulatory effect.

Mechanisms of Nonsteroid Hormone Action

Nonsteroid hormones typically operate according to a mechanism originally called the

second messenger hypothesis. According to this concept, also called fixed-membrane-receptor

hypothesis, a nonsteroid hormone molecule acts as a “first messenger,” delivering its chemical

message to fixed receptors in the target cell’s plasma membrane.

The second messenger mechanism produces target cell effects that differ from steroid

hormone effects in several important way. First, the cascade of reactions produced in the

second messenger mechanism

greatly amplifies the effects of

the hormone. Thus the effects of

many nonsteroid hormones are

disproportionally great when

compared to the amount of

hormone present. Recall that

steroid hormones produce

effects in proportion to the

amount of hormone present.

Also, the second messenger

mechanism operates much

more quickly than steroid

mechanism. Many nonsteroid

hormones produce their full

effects within seconds or

minutes of initial binding to the

target cell receptors—not the

hours or days sometimes seen with steroid hormones.

In the figure, a nonsteroid hormone binds to a fixed receptor in the plasma membrane of

the target cell. The hormone-receptor complex activates the protein and the activated protein

reacts with a certain nucleotide, which in turn activates the membrane-bound enzyme. The

activated membrane-bound enzyme removes phosphates from ATP, converting it to cyclic

adenosine monophosphate (cAMP). cAMP activates or inactivates an enzyme that will activate

intracellular enzyme. These activated enzymes then influence specific cellular reactions, such

as glycogen breakdown, thus producing the target cell’s response to the hormone

The nuclear receptor mechanism

Not all steroid hormones operate according to the second messenger.

Thyroxine (T4) and triiodothronine (T3) are small iodinated amino acids that apparently

enter their target cells and bind to receptors already associated with a DNA molecule

within the nucleus of the target cell. Formation of a hormone-receptor complex triggers

transcription of mRNA and the synthesis of new enzymes in a manner similar to the steroid

mechanism.

REGULATION OF HORMONE SECRETION

It is usually part of a negative feedback loop

Responses that result from the operation of feedback loops within the endocrine system

are called endocrine reflexes.

The simplest mechanism operates when endocrine cell is sensitive to the physiological

changes produced by its target cells

Another mechanism that may influence the secretion of hormones by a gland is input from

the nervous system

Although the operation of long feedback loops tend to minimize wide fluctuations in

secretion rates, the output of several hormones typically rises and falls dramatically within

a short period. For example, the concentration of insulin—a hormone that can correct a

rise in blood glucose concentration—increase to a high level just after a meal high in

carbohydrates. The level of insulin decreases only after the blood glucose concentration

returns to its set point value. Likewise, threatening stimuli can cause a sudden dramatic

increase in the secretion of epinephrine from the adrenal medulla as part of the fight-or-

flight response.

DISORDERS AND DISEASES OF ENDOCRINE SYSTEM

Hypersecretion- production of too much hormone.

Gigantism- abnormal rapid rate of skeletal growth.

Acromegaly-a condition in w/c cartilage is still left in the skeleton continuous

to form new bone.

-result in hypersecretion after skeletal fusion.

- may result from pituitary tumor, abnormally onset of puberty.

Hyposecretion- production of too little hormone.

Pituitary Dwarfism- stunted body growth.

-may result to disruption of reproduction, kidney function, overall

metabolism.

ANTIDIURETIC Hormone(ADH) Abnormalities

Diabetes insipidus- hyposectretion of Antidiuretic hormone(ADH).

-abnormal production of large amounts of urine.

THYROID Hormone Abnormalities

Graves diseases- hypersecretion of thyroid hormone w/c is thought to be an

autoimmune condition.

-leads to weight loss, nervousness, increased in heart rate, and

exophthalmos- protrusion of the eyeballs resulting from edema of tissue at

the back of the eye socket.

Cretinism- hyposecretion of thyroid hormone during growth years.

-characterized by a low metabolic rate, retarded growth and sexual

development, and possibly mental retardation, decreased metabolic weight,

loss of hair, yellow dullness of the skin, and myxedema-swelling(edema) and

firmness of the skin caused by accumulation of mucopolysaccharides in the

skin.

PARATHYROID Hormone Abnormalities

Hyperthyroidism- leads to increase in blood calcium levels and possible

development of osteoporosis and kidney stones due to elevation of

parathyroid hormone.

Hypocalcemia- too much tissue is removed that results to drop in PTH below

normal limits.

-cryopreservation- deep freezing, of the removed tissue of 1 year.

ADRENAL CORTICAL Hormone Abnormalities

Aldosteronism- hypersecretion of aldosterone that leads to increased water

retention and muscle weakness resulting from K ion loss.

Virilizing tumors-tumor of the adrenal cortex due to hypersection of

androgens. Also it increase the blood level of male hormones.

Cushing syndrome- the hypersecretion of cortisol from the adrenal cortex

-also had the characteristics of moon face and thin, reddened skin.

DIABETES MELLITUS

-most common endocrine disorders.

-result when the pancreatic islets secrete too little insulin, resulting in increased

levels of blood glucose.

Insulin resistance- the inability of fat, muscle, and other cells to respond

normally to insulin and permit the entry of the sugar.

Insulin insensitivity- the opposite of insulin resistance.

Hyperglycemia- the chronic elevation of blood glucose levels.

Glycosuria- spilling over of sugar into the urine.

Polyuria- increased urine production.

Polydipsia- excessive and ongoing thirst.

Polyphagia-intense and continuous hunger.

Diabetic ketoacidosis- accumulation of ketone bodies in the blood.

Types of Diabetes Mellitus

a. Type 1(juvenile-onset diabetes)- usually strikes before 30 years of age.

- Also called the insulin-dependent diabetes mellitus(IDDM).

- An autoimmune disease usually triggered by some type of viral infection in

genetically susceptible individuals

b. Type 2(non-insulin-dependent diabetes mellitus)

- Most common form of diseases.

- Often occurs after age 40 years.

- A specific gene defect.

THYROID DISORDERS:

Euthyroidism- the thyroid gland is functioning normally.

Hyperthyroidism- increased secretion of the gland’s hormone.

Hypothyroidism- decreased section of the gland’s hormone.

GOITER

a. Endemic goiter- nutritional iodine deficiency.

b. Sporadic goiter- not restricted to any geographical area. Major causes include

the following:

- Genetic defects resulting in faulty iodine metabolism

- Ingestion of large amounts of goitrogens such as cabbage soybeans and

spinach.

- Ingestions of medicinal goitrogens such as glocorticoids, dopamine, lithium.

HYPOTHYROIDISM

-a deficiency of TH resulting in slowed body metabolism,

Decrease heat production and decreased oxygen consumption by the tissues.

Primary hypothyroidism

-TH levels are low and TSH levels are elevated.

*Hashimoto’s disease- most common form of primary-autoimmune

hypothyroidism.

Secondary hypothyroidism

-insufficient stimulation of a normal thyroid gland, results decreased

TSH levels.

Tertiary or central hypothyroidism

-develops if the hypothalamus cannot produce TRH and TSH.

Subclinical hypothyroidism

-diagnosed with an elevated TSH level but a normal to low normal T4

level.

HYPERTHYROIDISM

-Excessive secretion of TH.

Thyroid storm(Thyrotoxicosis)

-potentially fatal acute episode of overactivity characterized by high

fever, severe tachycardia , delirium, dehydration, and extreme

irritability.

*Thyroidectomy-removal of the thyroid gland; may be total or partial.

THYROIDITIS

-inflammation of the thyroid gland.

Hope this movie helps you more understand abput endocrine system.

http://www.youtube.com/watch?v=-S_vQZDH9hY

http://www.youtube.com/watch?v=D6mZaFG-W4A&feature=related

SOURCES:

INTERNET

http://biology.clc.uc.edu/courses/bio105/endocrin.htm http://www.emedicinehealth.com/anatomy_of_the_endocrine_system/page12_em.h

tm#authors_and_editors http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookendocr.html

https://www.healthtap.com/#topics/endocrine-system-trivia

http://www.scribd.com/doc/25408619/PATHO-CH30-Organization-and-Control-of-the-Endocrine-System-Porth

http://t1.gstatic.com/images?q=tbn:ANd9GcQjaeNC1cU6E7Hhj2ULQJuG7p173rJWubMQ-hR7z0Whi9f3_iiCow

http://t2.gstatic.com/images?q=tbn:ANd9GcTmIG-tvPswIMmKUwb1eDEKNGaGPCuLqqOG4YPoXiRAxSDJdQw-CA

(n.d.). Retrieved from http://www.thepepproject.net/

(n.d.). Retrieved from http://www.google.com/

(n.d.). Retrieved from http://www.thepepproject.net/

(n.d.). Retrieved from http://www.google.com/

(n.d). Retrieved from

http://www.youtube.com/results?search_query=ENDOCRINE+SYSTEM&oq=ENDO

CRINE+SYSTEM&gs_l=youtube.3..0l10.54286.55157.0.55677.14.6.0.0.0.2.403.1161.

1j2j2j0j1.6.0...0.0...1ac.1.hcuMCLMWh84

Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

BOOKS

Thibodeau, G. A., & Patto, K. T. (2003). Anatomy and Physiology (5th editon ed.). Mosby.

Black, J. M., & Hawks, J. H. MEDICAL-SURGICAL NURSING (18TH ed.).

Thibodeau, G. A., & Patton, K. T. (2003). Anatomy and Physiology (5th editon ed.). Mosby.

Thibodeau, & Patton. Anatomy and Physiology (18th ed.).

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